This invention was made in the course of, or under a contract with the United States Energy Research and Development Administration, or its predecessor the United States Atomic Energy Commission.
Tritium with a half-life of 12.36 years and characterized by beta decay with an 18.6 KeV maximum energy has been considered one of the most innocuous of fission produced radionuclides. Along with .sup.59 Ni and .sup.55 Fe, it has a maximum permissible body burden of 1 mc, the highest value listed in the recommendations of the International Commission on Radiological Protection. Because of the low energy and penetration power of the beta particle associated with its decay, tritium does not pose a significant external radiation hazard. However, tritiated water and its vapor can be taken into the body by skin penetration. The retention of tritium in the body is dependent on the chemical form in which it enters. Thymidine, a specific precursor of deoxyribonucleic acid (DNA) is incorporated preferentially in the nuclei of cells. The probability of genetic and somatic damage from tritium exposure is enhanced when tritium is ingested as tritiated thymidine.
The natural abundance of tritium is exceedingly small, and has been estimated as approximately 1 tritium atom per 10.sup.17 hydrogen atoms in ordinary water. Other major sources of tritium are nuclear weapons testing, nuclear power plants, and nuclear fuel reprocessing operations. The natural annual tritium production has been assessed as 4 to 8 megacuries which would give rise to a steady-state tritium inventory of 70 to 140 megacuries. On the basis of present projections, the rate of production of fission-produced tritium would begin to exceed the rate of natural tritium production by about 1990. The development of thermonuclear power, while rather remote in the near future, is expected to significantly increase tritium inventories and management problems. The amount of tritium produced in thermonuclear reactions is several orders of magnitude higher than the amount of tritium produced by an equivalent quantity of fission energy.
It can presently be argued that on a global scale tritium production poses no problems. An inventory of 100 megacuries could be dissolved in the top 75 meters of the world's oceans to give a concentration of 3.7 .times. 10.sup.-.sup.10 .mu.Ci/ml. This is significantly less than the present maximum permissible concentration of 3 .times. 10.sup.-.sup.3 .mu.Ci/ml. However, local tritium concentrations may become problematic. A major fraction of the fission-produced tritium will be released during fuel reprocessing and there is a strong economic incentive to increase the size of other plants as the nuclear industry expands. A 10 ton/day reprocessing plant may have to dispose of 6,000 Ci/day requiring 2 .times. 10.sup.9 liters of water per day to dilute to the mpc level.
Present methods for fixing tritiated water include a solidification process involving ureaformaldehyde (UF) or a cement process. Solidification by the former process may result in the presence of unreacted acidic catalyst which may attack the container. The latter produces a product which is porous so that the final product must be kept dry to avoid leaching.